考虑IMC影响的PBGA无铅焊点温度循环有限元数值模拟

Numerical simulation of PBGA lead-free solder joints with consideration of IMC layer under thermal cycling condition

采用ANSYS统一Anand粘塑性本构方程描述SnAgCu焊点非弹性形变.对考虑IMC的PBGA焊点与不考虑IMC的PBGA焊点在温度循环载荷作用下的应力应变响应进行分析比较.结果表明,远离中心位置的外侧焊点承受更大的应力应变;在温度循环加载过程中IMC层积累了较大的应力;由于IMC层的硬脆性材料特性,应力不会通过塑性形变释放,使焊料在高应力IMC界面发生较大的塑性形变;IMC焊点高应力集中区的应力应变迟滞回线所代表的应变能高于不考虑IMC的焊点,导致其热疲劳寿命远低于不考虑IMC的焊点,与实际温度循环试验结果更为接近.

An unified viscoplastic constitutive Anand model was utilized to describe the inelastic deformation behavior for SnAgCu solder alloy in PBGA package and to analyze the stress-strain response in the solder joints under thermal cyclic loading.The results demonstrated that the stresses and strains of corner solder joints were higher than those of inner solder balls.The equivalent plastic strain of the solder alloy near the IMC layer increased dynamically due to the properties of the brittle IMC layer.The strain energy represented in the stress-strain hysteresis loop of the IMC solder joints in high stress concentration region was higher than that of non-IMC solder.The simulation results revealed that the IMC layer significantly affected thermal fatigue reliability of the solder joints.The thermal fatigue lifetime using the Anand model was basically consistent with experimental data.